This invention pertains to the field of urethane catalysts. More particularly, this invention relates to the use of certain specific amine compounds as urethane catalysts.
The use of a catalyst in preparing polyurethanes by the reaction of a polyisocyanate, a polyol and perhaps other ingredients is known. The catalyst is employed to promote at least two, and sometimes three major reactions that must proceed simultaneously and competitively at balanced rates during the process in order to provide polyurethanes with the desired physical characteristics. One reaction is a chain-extending isocyanate-hydroxyl reaction by which a hydroxyl-containing molecule is reacted with an isocyanate-containing molecule to form a urethane. This increases the viscosity of the mixture and provides a polyurethane containing secondary nitrogen atoms in the urethane groups. A second reaction is a cross-linking isocyanate urethane reaction by which an isocyanate-containing molecule reacts with a urethane group containing a secondary nitrogen atom. The third reaction which may be involved is an isocyanate-water reaction by which an isocyanate-terminated molecule is extended and by which carbon dioxide is generated to blow or assist in the blowing of foam. This third reaction is not essential if an extraneous blowing agent, such as a halogenated, normally liquid hydrocarbon, carbon dioxide, etc., is employed, but is essential if all or even part or the gas for foam generation is to be generated by this in situ reaction (e.g. in the preparation of "one-shot" flexible polyurethane foams).
The reactions must proceed simultaneously at optimum balanced rates relative to each other in order to obtain a good foam structure. If carbon dioxide evolution is too rapid in comprison with chain extension, the foam will collapse. If the chain extension is too rapid in comparison with carbon dioxide evolution, foam rise will be restricted, resulting in a high density foam with a high percentage of poorly defined cells. The foam will not be stable in the absence of adequate crosslinking.
Many of the catalysts used today are tertiary mono and di-amines. Among these are N,N,N',N'-tetramethylethylene diamine, N,N-dimethyl cyclohexylamine, N-methylmorpholine and the highly used bis(2-dimethylaminoethyl)ether, N-methyldicyclohexyl amine and 1,4-diazabicyclo[2.2.2] octane ("triethylene diamine"). Other typical amines used in forming polyurethanes are described in U.S. Pat. Nos. 4,012,445; 3,925,268; 3,786,005; 4,001,223; 4,048,107; 4,038,210; 4,033,911; 4,026,840; 4,022,720 and 3,912,689.
Some of the presently used tertiary amines leave a residue in the foam and thereby impart an undesirable odor to the resultant product. Still further, certain catalytic compounds, especially the alkyl tertiary amines, which meet specifications in the area of odor do not yield foams within desired tack-free time due to their low activity. The need for rapid gel, tack-free and final cure times are required in the formation of foam products in many of today's processing operations.
Commercial production of urethane foams, especially flexible foams, has undergone major change from production of domed buns to flat-top buns. Conventional domed buns normally require trimming and removal of the "dome" which translates into a 15 to 20% loss or product. Moreover, foam density and uniformity often vary and finishing costs of such doomed buns makes such processing less desirable than the newer flat-top bun process as is described in Plastic Technology, Vol. 24, No. 13, pages 57-62, 1978 and in Plastics and Rubber Processing Vol. 2, No. 11, pages 30-32, 1977, said description incorporated herein by reference.
Processing designs associated with achieving flat-top buns have placed increased demands on the chemistry of polyurethanes, particularly those related to the catalysts necessary to provide a proper balance in polymerization and blowing. It is necessary for the catalyst material or system to be capable of exhibiting a reactivity profile comprised of delayed creaming, delayed and controlled gellation/polymerization, controllable rise and rapid cure. Stated another way, the catalyst must permit gelation or viscosity build-up not to occur too quickly. Should this occur, there would be increased stress placed on the foam possibly causing splitting and/or cell collapse. Therefore, delayed action catalyst is desired since it causes less strain on the forming foam and facilitates molding the rising bun into a square shape. The foam must form in a moderate, uniform manner. Moreover, despite the slower cream and moderate rise time, the tack-free time must be suitable to permit handling of the foam in short time periods as well as to improve the physical properties of the resultant foam.
It is greatly desired to have a catalyst for forming foam polyurethanes which does not result in a product having malicious odor from the residue catalyst, which provides for the formation of a substantially uniform foam, which is capable of providing a suitable reaction profile for normal processing which produces a uniform, odor-free foam, which is capable of providing a reaction profile that is compatible with the requirements of the flat-top bun process and which is capable of forming tack-free products within a very short period of time.